Daylight saving time
What is daylight saving time?
A twice-a-year decision to shift the clock one hour so evening daylight lasts longer in summer. Not every place does it. When they do, the offset from UTC changes, and so does the sunrise time on the clock — not the sunrise in the sky. The sunrise pages follow the zone’s real rules.
The sky does not change
On the spring-forward night, 2:00 a.m. becomes 3:00 a.m. You lose an hour of sleep. The Sun still rises when the Earth has turned far enough. Only the number on the clock jumped.
Arizona (mostly) and Hawaii do not do this. Most of Europe does. That is why a world clock has to know the rules, not just a fixed offset.
Get more on this
Why the clock, not the Sun
The original pitch was to move an hour of daylight from the morning, when fewer people are out, to the evening. Whether it saves energy is argued. What it definitely does is change every offset from UTC for a few months, which is why a sunrise table that ignored DST would be an hour wrong all summer.